1. Field of the Invention
The present invention relates to a cooling system for a variety of electronic packages that are used in electronic equipment such as electronic computers, workstations, personal computers and the like.
2. Description of the Related Technology
As is well known, electronic equipment such as electronic computers, workstations, personal computers and the like are equipped with circuit boards on which are mounted a variety of electronic packages such as CPUs (central processing units) as represented by MPUs (microprocessor units) and MCMs (multi-chip modules). In recent years, the electronic packages are becoming more dense and, hence, generate more heat when they are in operation. It need not be pointed out that in order to guarantee proper operation of the electronic packages and to extend their life, it is necessary to suitably cool the electronic packages to maintain their temperatures to lie within predetermined ranges.
In order to cool the above-mentioned highly sophisticated electronic packages, it has heretofore been proposed to use, for example, a heat sink 10 with a cooling fan as shown in FIGS. 15(a), 15(b) and 15(c). The heat sink 10 with cooling fan comprises a heat sink plate 12, a small electric motor 14 mounted on the center of the heat sink plate 12, and a fan 16 attached to an output shaft of the small electric motor 14. Furthermore, a number of heat-radiating fins 18 are extending from the heat sink plate 12 and are nearly radially arranged so as to surround the fan 16. As will be obvious from FIGS. 15b and 15c, the heat sink 10 with cooling fan is directly attached to a highly dense electronic package 20. Upon driving the small electric motor 14, therefore, the highly sophisticated electronic package is efficiently cooled. That is, upon rotating the fan 16, an air flow is produced among the heat-radiating fins 18 as indicated by arrows in FIGS. 15(a) and 15(b), whereby the heat conducted to the heat-radiating fins 18 from the highly dense electronic package 20 through the heat sink plate 12 is efficiently radiated.
FIG. 16 illustrates another conventional cooling system in which a heat conducting plate element 24 is attached onto the highly dense electronic package 20 that is mounted on a circuit board 22. A pair of heat pipes 26 extend from the heat conducting plate element 24, and many heat-radiating fins 28 are attached to the ends of the pair of heat pipes 26. According to the prior art, the heat is efficiently conducted from the heat conducting plate element 24 to the heat-radiating fins 28 through the heat pipes 26, and the highly dense electronic package 20 is favorably cooled.
It has been pointed out that the conventional cooling system shown in FIGS. 15(a), 15(b) and 15(c) has a problem in that the heat sink with cooling fan is itself bulky. For example, the junction temperature of a highly dense electronic package (MPU: microprocessor unit) having a square shape of a side of about 4 cm that generates 15 watts of heat can be lowered to be not higher than 85.degree. C. at an ambient temperature of 40.degree. C. When the heat is generated in further increased amounts, however, the heat sink with cooling fan of a larger size must be employed to guarantee the operation of the MPU maintaining a temperature of 85.degree. C. In the vicinities of a place where the highly dense electronic package is mounted, however, no space is available for installing such a large heat sink with cooling fan. In order to cope with an increased amount of heat without using the heat sink of a large size, it can be contrived to employ a liquid cooling system requiring, however, conduits and coolant feeding device resulting in a considerable increase in the cost for cooling.
The conventional cooling system of the type shown in FIG. 16 has a problem in that a forced air cooling is necessary to assist the radiation of large amounts of heat from the heat-radiating fins and that the cooling fan must be provided separately from the cooling system. When the housing of an electronic equipment is provided with a cooling fan for forced air cooling, the place for installation must be determined in relation to a place where the heat-radiating fins are formed, imposing a limitation on the freedom for designing the electronic equipment as a whole. There also arise problems in that there is no freedom in the combination of the cooling fan and the heat-radiating fins, it is not easy to improve the conduction of heat through the fins, and the heat-radiating fins themselves must be formed in a large size. So far, no particular attention has been given to space for laying out the heat pipes and heat-radiating fins in the housing.